1. Field of the Invention
The present invention relates to the hydroxylation of phenols or phenol ethers with hydrogen and, more especially, to the hydroxylation of such phenols/phenol ethers with hydrogen peroxide in the presence of a catalytically effective amount of particular MFI zeolite.
2. Description of the Prior Art
The hydroxylation of phenol or substituted phenols with hydrogen peroxide, to prepare diphenols, is known to this art.
French Patent No. 69/45,467, published under No. 2,071,464, describes a process in which the reaction is catalyzed by a strong acid such as, for example, perchloric acid or sulfuric acid.
German Patent No. 2,410,742 describes a process similar to the above, in which hydrogen peroxide is employed in the form of a virtually anhydrous organic solution.
These two processes are quite attractive, and the first process is employed industrially.
However, over the past few years, an attempt has been made to catalyze the hydroxylation reaction using solids which are not dissolved in the reaction medium, in order to simplify their separation from such medium and their possible recycling, and to avoid the saline biproducts which most often are formed during the removal of the dissolved acid catalysts.
Thus, French Patent Application No. 81/17,023 (published under No. 2,489,816) recommends the use of titanium silicalite as a heterogeneous catalyst for the hydroxylation of aromatic compounds with hydrogen peroxide
In fact, this catalyst presents extreme difficulties in respect of process reproducibility. In addition, the finely divided size of the catalyst particles makes their separation from the reaction medium very difficult and their recycling problematical whereas, in an industrial process, it is essential to be able to recycle an expensive catalyst.
To obviate this problem of separation of the catalyst, it has been proposed, in the European patent application published under No. 200,260, to use agglomerates of these fine particles of titanium silicalite.
Serious need continues to exist in this art, however, for a process for the heterogeneous catalysis of the hydroxylation of phenols or phenol ethers with hydrogen peroxide which can be carried out on an industrial scale under economically acceptable conditions.